The present invention relates to transparent coatings for substrates. More particularly, the invention relates to transparent coatings that protect substrates from the adverse effects of contact with water. Yet more particularly, the invention relates to a transparent coating for a substrate, such as canvas, paper, cardboard or the like, that has an image printed or otherwise recorded thereon, the coating effective to repel water and to prevent smearing or running of inks that are not water-fast, such as, for example, water-based inks used in ink-jet printers. In accordance with the invention, a transparent coating is affixed on the substrate such that the coating provides a water-impervious protective barrier over the substrate.
By way of background, a great deal of attention has been given in recent years to improving and developing new compositions, devices and methods for printing or otherwise recording high quality characters, images and the like on substrates such as canvas, paper, cardboard, and the like. Particularly notable is technology involving ink-jet recording techniques. An ink-jet recording system (also referred to herein as an xe2x80x9cink-jet printerxe2x80x9d) is a recording system in which fine ink droplets are formed by one of various methods, and the ink droplets are directly applied to a recording medium such as paper.
In an ink-jet printer, liquid ink is ejected onto a recording medium as flying particles from nozzles (orifices) of a very small diameter, so that flying particles of the ink adhere onto the recording medium to thereby form characters, images and the like. Ink-jet printing therefore involves placement, in response to a digital signal, of small drops of a fluid ink onto a surface to form an image without physical contact between the printing device and the surface.
An ink-jet recording technique is advantageous in that less noise is generated during recording compared to other recording techniques, and images of high resolution are obtained at a high speed by using heads with a high degree of integration. Indeed, this ability to produce high resolution images, in combination with the capabilities of modern computers to facilitate the creation and duplication of images digitally, has led to the widespread use of ink-jet printers in the production and reproduction of artwork. A form of artwork that has become extremely popular of late involves giclee printing, in which a computer image of a work of art is made and then printed onto canvas, paper, cardboard or the like using a high quality ink-jet printer. Pieces made in this manner are then often sold, optionally with the artists signature thereon. Works of art, including paintings, sketches and other art forms can be converted to a digital file, for example, using a scanner, and then printed using an ink-jet printer to make replicas of the artwork. Alternatively, artwork can be created originally using a computer and then can be printed in a similar manner.
The method of drop generation varies among the different ink-jet technologies and can be used to classify ink-jet printing into two major technology types, continuous (CIJ) and drop-on-demand (DOD). In DOD printing systems, liquid ink droplets are propelled from a nozzle by heat (thermal or bubble ink-jet) or by a pressure wave (piezo ink-jet). All the ink droplets are used to form the printed image and are ejected as needed, xe2x80x9con demand.xe2x80x9d Thermal or bubble jet inks typically are based on water and glycols. In CIJ printing systems, a continuous stream of liquid ink droplets is ejected from a nozzle and is directed, with the assistance of an electrostatic charging device in close proximity to the print head, either to a substrate to form a printed image or to a recirculating system.
Presently, the most common ink-jet recording techniques employ, as a recording liquid, ink that is prepared by dissolving various water-soluble dyes in water or a mixture of water and an organic solvent. The following properties of such an ink composition are desired:
(a) high quality printing (edge acuity and optical density) of text and graphics on substrates,
(b) short dry time of the ink on a substrate such that the resulting printed image is not smudged when rubbed or offset onto a subsequent printed image placed upon the print,
(c) good jetting properties exhibited by a lack of deviation of ink droplets from the flight path (misplaced dots) and of ink starvation during conditions of high ink demand (missing dots),
(d) resistance of the ink after drying on a substrate to water and to abrasion,
(e) long-term storage stability (no crust formation or pigment settling) and
(f) long-term reliability (no corrosion or nozzle clogging).
Often, the inclusion of an ink component meant to satisfy one of the above goals could have a detrimental impact upon another. For example, the inclusion of an aqueous resin or other polymer in the ink composition can improve the water resistance of the ink on a substrate after drying and the affinity of pigments to the substrate. In this regard, the use of lignin binders in ink-jet inks has been described. It has been reported that unmodified lignin may be used in conjunction with other polymers in such an ink. However, the addition of a polymer sufficient to fix the pigments on the substrate increases the viscosity of the recording liquid, and problems in practicality of ink discharge stability arise due to the increase in energy required for ink discharge of the inkjet. In addition, the polymer can cause a reduction in the print quality and optical density, as well as impair jetting properties and long-term storage stability. Thus, most commercial ink-jet inks represent a compromise in an attempt to achieve at least an adequate response in meeting the above listed goals.
An ink-jet printer generally employs inks of the type obtained by dissolving various dyestuffs in water or in an organic solvent. Water-based inks containing water-soluble recording agents are used in many ink-jet printers because they have suitable ejection and printing characteristics and because they have desirable characteristics from the viewpoints of safety, odor and the like. These inks are typically composed of a water-soluble dye or pigment, a water-soluble organic solvent (anti-crusting agent) used for preventing clogging by drying within an ejection nozzle, water, and optional components such as a penetrant, a dye-dissolving aid and a mildew-proofing agent. Since water soluble dyes with high solubility in water are generally used, the water resistance of the inkjet recorded materials is generally low and the dye on the recorded material may be easily smudged when water is spilled onto it. The use of water-soluble dyes, therefore, often causes a problem in water resistance of recorded images owing to the fact that the ink is water-soluble. In other words, if recorded images are moistened with rain, sweat or drinking water, they are likely to smear, blot, blur or disappear.
A wide variety of attempts have been made to address the problem of smearing and running ink that occurs when a recorded image generated using a water-based ink is contacted by water or other elements. For example, attempts have been made to improve the inferior water resistance by changing the structure of the dye or preparing recording liquid with high basicity. Also, attempts to improve water resistance by causing a reaction between the recording paper and recording liquid have been made. These methods have made remarkable effects for special recording papers but lack versatility in that they are limited to special recording papers and, quite often, the water-resistant quality of the recorded material is insufficient when recording papers other than those specially prescribed are used.
Other attempts to address the problem of smearing and running ink that occurs when a recorded image is contacted by water or other elements involve the placement of a barrier layer over the image. Examples include dry mounting, or laminating, which includes adhering a preformed plastic film over the image, and application of various volatile solvent-based compositions over the image. Such attempts, however, suffer from numerous disadvantages, including, for example, high labor requirements; requirements for large and expensive equipment; difficulty achieving good quality, especially for large images; significant health and environmental implications relating to the use of volatile, often toxic, solvents; and the like.
There is a continuing need for further developments in the field of printed images, especially ink-jet printed images, to improve the water fastness of printed images. The present invention addresses this need.
Provided by the present invention are compositions and techniques for protecting a substrate by placing a transparent, water-impervious coating over the substrate.
One form of the present invention is a unique composition that can be applied to a surface and heated to provide a transparent, water-impervious coating.
A further form of the present invention includes a technique for protecting a substrate by applying a viscous heat-curable composition to the substrate and heating the composition to provide a transparent, water-impervious coating on the substrate.
Further forms, embodiments, objects, features, and aspects of the present invention shall become apparent from the description contained herein.